As disclosed in PCT International Publication WO99-07990, a fuel pump is provided with a substantially disc-shaped impeller that rotates within a casing. As shown in FIG. 9, a group of concavities 36a is formed in an upper face of the impeller 36, and the group of concavities 36a is formed along the circumference direction of the impeller 36 in an area located inwardly from an outer circumference 36d of the impeller 36 by a distance shown by “A” in FIG. 9. Each of concavities 36a extends in the radial direction by a distance shown by “B” in FIG. 9. The concavities 36a are repeated in the circumference direction, and adjacent concavities 36a, 36a are separated by a partitioning wall 36b. As shown in FIG. 11, a group of concavities 36e having the same configurations as the group of concavities 36a is formed in an lower face of the impeller 36
As shown in FIGS. 10 and 11, bottom portions of the pair of upper concavity 36a and lower concavity 36e are communicated with each other at the outer side region within the concavities 36a, 36e. The length of a through-hole 36c communicating the pair of upper concavity 36a and lower concavity 36e in the radial direction is shown as “C” in FIGS. 10 and 11. The distance “C” is formed within the distance “B” at the outer side.
A pair of grooves is formed at interior faces of the casing that houses the impeller 36, each groove being formed in an area directly facing each of the groups of concavities 36a, 36e and extending continuously in the direction of rotation of the impeller 36 from an upper flow end to a lower flow end. An intake hole passes through the casing to the upper flow end, and a discharge hole passes through the casing from the lower flow end.
When the impeller 36 rotates within the casing, fuel is drawn into the casing from the intake hole, is pressurized as it flows along the circumference direction within the casing, and then the pressurized fuel is discharged from the discharge hole.